This invention relates, in general, to large heat exchangers; and, in particular, to non-contact steam generators. Non-contact steam generators for purposes of the present invention may be defined as an apparatus for producing steam by passing hot gases through an enclosed duct so as to heat water/steam in fluid carrying tube bundles disposed across the duct. The hot gases may be produced by firing burners at the base of the steam generator or the hot gas may be the hot exhaust gas of a gas turbine as is found in a power plant arrangement known as a combined cycle power plant. One particular form of a steam generator is a heat recovery steam generator which may be formed of several sections constructed in modular fashion. Such sections are well known in the art as a preheater (low pressure economizer), economizer (high pressure economizer), evaporator and superheater. The economizer, evaporator and superheater may all be in fluid communication with a steam drum located outside the hot exhaust path. One such configuration is shown in U.S. Pat. No. 3,934,553 to Freeman et al and assigned to the assignee of the present invention. The aforementioned sections have all been mentioned in descending order with respect to the manner in which they are usually assembled in the steam generator. As the hot gas rises in the steam generator flow path, the temperature of the gas decreases. As the water descends through the steam generator tubes, the water/steam temperature rises; i.e., the two heat exchange mediums flow counter with respect to one another.
In the prior art, the heat exchange tubes were mounted in fixed tube support plates such that the tubes were allowed to expand thermally by sliding through the holes in the tube support. As will be later substantiated, this arrangement does not produce optimum results in the instance of unequal tube expansion which is not strictly in the axial direction, and may lead to a permanent warp in a tube bundle causing unsatisfactory performance and potential early failure of the tube bundle.